Field
The present invention relates to a method for manufacturing elastomeric material components of a tyre for vehicle wheels, comprising the following phases: feeding a continuous elongated element from a dispensing organ positioned adjacently to a toroidal support to apply said elongated element onto the toroidal support itself; conferring to the toroidal support a rotatory circumferential distribution motion about its own geometric axis of rotation, so that the elongated element is circumferentially distributed on the toroidal support; effect controlled relative transverse distribution displacements between the toroidal support arid the dispensing organ to form with said elongated element a component of a tyre defined by a plurality of turns positioned mutually approached and/or superimposed according to a pre-determined cross section profile to be conferred to said component.
Description of the Related Art
The manufacture of tyres for vehicle wheels provides for the formation of a carcass structure essentially comprising one or more carcass plies shaped according to a substantially toroidal conformation and presenting their axially opposite lateral edges engaged to respective circumferentially inextensible annular reinforcing elements, usually called “beads rings”.
On the carcass structure is applied, in radially exterior position, a belt structure comprising one or more belt layers shaped in a closed loop, essentially composed of textile or metal filaments appropriately oriented relative to each other and relative to the filaments belonging to the adjacent carcass plies.
In radially exterior position to the belt structure, a tread band is then applied, normally constituted by a strip of elastomeric material of suitable thickness.
It should be specified that, for purposes of the present description, the term “elastomeric material” indicates the rubber compound in its entirety, i.e. the set formed by at least a base polymer suitably amalgamated with reinforcing charges and process additives of various kinds.
Lastly, a pair of sidewalls is applied onto the opposite sides of the tyre being manufactured, each of which sidewalls covers a lateral portion of the tyre lying between a so-called shoulder area, located in proximity to the respective lateral edge of the tread band, and a so-called bead located in correspondence with the respective bead ring.
Traditional production methods provide essentially for the tyre components listed above first to be made separately from each other, then to be assembled in a tyre manufacturing phase.
The Applicant's current trend, however, it to employ productive methodologies which allow to minimise or, possibly, to eliminate the production and storage of semi-finished products.
In practice, the Applicant's research and development are oriented towards new process solutions that allow to produce individual components by forming them directly on the tyre being manufactured according to a pre-set sequence.
In this regard, manufacturing processes have been proposed which are aimed at obtaining determined tyre components, such as the tread band, the sidewalls others, by laying, onto a toroidal support bearing the tyre being manufactured, a continuous elongated element of elastomeric material having reduced section relative to that of the component to be obtained, and positioned to form, about the axis of rotation of the tyre, a plurality of turns consecutively approached and/or superposed thereby defining the component itself in its final configuration.
More specifically, U.S. Pat. Nos. 4,963,207 and 5,171,394 describe respectively a method and an apparatus wherein determined components of a tyre are obtained by laying on rigid toroidal support an elongated element of elastomeric material continuously fed from a dispensing organ associated to a volumetric extruder.
While the toroidal support is made to rotate about its own geometric axis, determining a circumferential distribution of the elongated element, the volumetric extruder is moved in such a way as to confer controlled displacements to the dispensing organ in a plane meridian to the toroidal support, thereby distributing the various turns formed by the continuous elongated element according to a pre-set arrangement.
U.S. Pat. No. 5,221,406 calls for the placement, around the toroidal support, of a plurality of volumetric extruders, each able to feed, by means of its own dispensing organ, a respective continuous elongated element to be selectively employed to obtain a determined component of the tyre.
The document GB 1,048,241 describes a method and an apparatus for manufacturing the sidewalls, the shoulders and the tread band of a tyre by winding a continuous ribbon-like element made of elastomeric material onto a toroidal support actuated in rotation about its own geometric axis. During the application, the toroidal support is made to rotate about an axis of revolution tangential to a median circumferential line of its profile in cross section, in such a way that the ribbon-like element is distributed on the outer surface of the toroidal support itself to form a series of turns set side by side and partially overlapping one another. The angular velocity imposed to the toroidal support about the axis of revolution is appropriately modified during the laying operation, to vary the degree of overlap of the consecutive turns and adequately to differentiate the thickness of the rubber layer formed by the turns in the different areas of the tyre.
In accordance with the present invention, it was found that if the peripheral velocity of the toroidal support in the point of application of an elongated element is controlled in such a way as to maintain a suitably greater value of the speed whereat the elongated element itself is fed by the dispensing organ, the adhesion of the applied elongated element is considerably enhanced, and considerable advantages are attained in terms of operative flexibility. In particular, the capability is achieved of suitably modifying the cross section dimensions of the elongated element to adapt it to the thickness of the component to be manufactured, in the various points of the cross section profile thereof.